Method for thermally drawing nanocomposite-enabled multifunctional fibers

ABSTRACT

A method of thermally drawing fibers containing continuous crystalline metal nanowires therein includes forming a preform comprising an inner core and an outer cladding, wherein at least one of the core and cladding has nanoelements dispersed therein. The preform is drawn through a heated zone to form a reduced size fiber. A second preform is then created from a plurality of fibers created from the reduced size fiber. The second preform is then drawn through the heated zone to form an elongated fiber containing continuous crystalline metallic nanowires therein having a maximum cross-sectional dimension of less than 100 nm. Optionally, a third or additional preforms are created from fibers made from the previous thermal drawing operation that are then drawn through the heated zone to form a fiber containing even smaller crystalline metal continuous nanowires therein. In some embodiments, only a single pass through the heated zone may be needed.

RELATED APPLICATION

This Application claims priority to U.S. Provisional Patent ApplicationNo. 62/110,363 filed on Jan. 30, 2015, which is hereby incorporated byreference in its entirety. Priority is claimed pursuant to 35 U.S.C.§119 and any other applicable statute.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under award number1449395, awarded by the National Science Foundation. The Government hascertain rights in the invention.

TECHNICAL FIELD

The technical field generally relates to methods and devices used in thethermal drawing of fibers having nanoparticles contained in the core,cladding, or both.

BACKGROUND OF THE INVENTION

Long fibers with embedded functionalities have great potentials fornumerous applications. Ongoing research on ultra-long functional fibersinclude, for example, microstructured photonic crystal fibers, opticalmicro/nano fibers, electronics in fibers, fiber-based metamaterials,fibers as a novel platform for sensing devices, studying chemicalreactions, multi-material functional fibers, and more recently fibers asa platform for fabrication of nanowires and nanoparticles. The trend ofcombining a multitude of functionalities into a single long fiberdemands the incorporation of a multiplicity of solid materials each withdisparate physical properties. Significant progress has been made alongthis direction by thermal drawing of macroscopic multi-materialspreforms. Materials that have distinctively different electrical andoptical properties are integrated into a single fiber by means of apreform-based thermal drawing technique. Various electronic andoptoelectronic devices have been realized in kilometer long fibers.Large-scale fabrics woven from such fibers have also been demonstrated.The capability of this technique towards scalable nanofabrication hasbeen explored, however, with mixed success.

There exists a strong demand for low-cost and scalable manufacturingmethods and techniques of these fibers having continuous nanowirescontained therein. For example, such nanowires may be made fromgenerally inert metals such as gold (Au), silver (Ag), and platinum (Pt)and used in short-haul electrical interconnect bundles and front-endsensing/recording multi-electrode arrays. Additional existing andemerging applications include, for instance, high resolutionsemiconductor/thin-film resistivity probes, electrical cellularphenotyping, neural/cardiac electrical signal recording, etc.,representing a large global commercial market. Despite the hugepotential economic and technological impact that high-volume productionof fibers with continuous metallic nanowires will bring about, there hasbeen little success for their reliable and scalable manufacturing;mostly due to the fluid instability induced by the low viscosity ofmolten metals and its large interfacial energy with the cladding.

Thermal drawing is a very promising approach to realize volume andlow-cost nano-production of fibers with nanowires without harnessingcostly lithography. However, there are significant scientific andmanufacturing barriers that must be overcome. A successful thermaldrawing of fibers from a macro preform made of multi-materials isfundamentally limited by at least the following constraints: (1) theviscosity of the most viscous constituent material (i.e. the cladding)should fall between 10^(3.5) and 10⁷ Poise at the drawing temperature inorder for the process to be controllable. Amorphous materials, such asglass and polymers, are typically used as the support (cladding) tocontain other core materials for cross-sectional stability; (2) thesoftening or melting temperature of the core material(s) should be lowerthan or overlap with the drawing temperature. If a crystalline materialis to be drawn, low vapor pressure is desired and its boiling should beavoided; (3) chemical reactions between the cladding and core materialsshould be avoided unless intentionally designed (e.g., for in-fibersynthesis purposes); (4) it is desired that cladding and core materialsexhibit good adhesion/wetting with each other during and after drawingto avoid cracks, bubbles and fluid instability of the core material(s);and (5) the cladding and core materials should have relativelycompatible thermal expansion coefficients in the temperature range up tothe drawing temperature.

These constraints pose severe challenges to find suitable materialcombinations for multifunctional polymers or glass fibers drawn withmetal nanowires. At present, most crystalline metal nanowires or evenmicro-wires are beyond the capability of current manufacturingtechniques, due to the fluid instability induced by a low viscosity ofmolten metals and the large interfacial energy with the claddingmaterials.

Fibers with metal microwires are routinely produced by thermal drawing.The softening temperature of the cladding determines the types of metalsthat can be drawn within. Low melting temperature metals such as tin(Sn), bismuth (Bi), indium (In), and their respective alloys have beenthermally drawn in polymer cladding (e.g., polyethersulphone (PES),polysulfone (PSU), and polyethylenimine (PEI) at which the softeningtemperature is below 300° C.). The resulting metal fibers withrectangular or circular cross sections have critical dimensions rangingfrom tens to hundreds of micrometers; they are not in the nanometerrange. Fibers with metal microwires are also thermally drawn along withother functional materials (usually semiconductors or conductivepolymers) and serve as conductive electrodes in multi-materialfunctional fibers, which are in turn utilized as, for example, 1Dphotodetectors, thermal sensors, piezoelectric transducers, chemicalsensors, and capacitors. The smallest diameter reported for metal-basedwires that can be reliably drawn into infinitely long arrays is around 4μm and is achieved from a low melting temperature Sn_(0.95)Ag_(0.05)alloy with PES cladding. See Yaman et al., Arrays of indefinitely longuniform nanowires and nanotubes, Nature Materials, vol. 10, pp. 494-501(2011). Beads, discontinuities, and structural deformation were observedupon further size reduction. Others have demonstrated that thermallydrawn functional fibers embedding in wires with diameter approaching 1μm. See Tuniz et al., Fabricating Metamaterials Using the Fiber DrawingMethod, Journal of Visualized Experiments, vol. 68, 2012.

Higher melting temperature metals such as Au, copper (Cu), zinc (Zn),and their respective alloys require cladding materials with highersoftening temperatures. Pyrex glass (with softening point ˜800° C.) andfused silica (with softening point ˜1700° C.) are the materials ofchoice in this regime, though not excluding their usage to draw metalswith low melting temperature. In fact, larger sized, metal microwirefabrication by thermal drawing in a glass cladding, known as theTaylor-wire process, has been in practice for decades. However, similarto the case with polymer cladding, manufacturing reliability suffers asthe diameter of metal wire approaches less than 1 μm. Au microwires of 4μm diameter have been fabricated over a length of several centimetersand this continuous length shrank to ˜20 μm as their diameter reduced to260 nm. See Tyagi et al., Plasmon Resonances on Gold Nanowires DirectlyDrawn in A Step-index fiber, Optics Letters, vol. 35, pp. 2573-2575(2010). Pb—Sn alloys and Bi nanowires (drawn in glass cladding) withdiameter down to 50 nm were reported with a length reaching 1 m with noexperimental evidence provided to support their continuity over theclaimed 1 m drawn length. See Badinter et al., Exceptional Integrationof Metal or Semimetal Nanowires in Human-hair-like Glass Fiber,Materials Letters, vol. 64, pp. 1902-1904 (2010). Similarly, fabricationof discontinuous Cu_(0.93)P_(0.07) with a diameter of 500 nm has beenreported using Pyrex glass cladding. See Zhang et al., Mass-Productionsof Vertically Aligned Extremely Long Metallic Micro/Nanowires usingFiber Drawing Nanomanufacturing, Advanced Materials, vol. 20, pp.1310-1314 (2008). On the other hand, and again being consistent withthat of using polymer cladding, thermally drawn continuous Cu microwireof 4 μm in diameter has been demonstrated which enables single modevisible light guidance by metallic reflection in a photonic crystalfiber See Hou et al., Metallic Mode Confinement in MicrostructuredFibres, Optics Express, vol. 16, pp. 5983-5990 (2008).

Fiber drawing via laser-based heat source pulling of short pieces of Ptmicrowires has been used to fabricate quartz-sealed Pt nanowires. Theresultant fibers were tapered down to 10 nm in diameter yet with alength of only 5 mm. See Percival et al., Laser-pulled UltralongPlatinum and Gold Nanowires, RSC Adv., vol. 4, pp. 10491-10498 (2014).Since such tapering method is confined to a narrow (length) region ofwires, it is hard to extend it to pull wires that are tens ofcentimeters long. Alternatively, a polyol process, which is thesynthesis of metal-containing compounds in ethylene glycol, was used tofabricate Ag nanowires with length up to 230 μm and diameter of 60-90nm. See Araki et al., Low Haze Transparent Electrodes and HighlyConducting Air Dried Films with Ultra-long Silver Nanowires Synthesizedby One-step Polyol Method, Nano Research, vol. 7, pp. 236-245 (2014) andJiu et al., Facile Synthesis of Very-long Silver Nanowires forTransparent Electrodes, J. Mater. Chem. A, vol. 2, pp. 6326-6330 (2014).Polyvinylpyrrolidone (PVP) and ethylene glycol (EG) were used as thecapping and reducing agent, respectively, which also mandated a few moresteps in manufacturing.

From the above-described literature citations, despite the fact thatreliable drawing of indefinitely long amorphous semiconductor andpolymer nanowires has been achieved, it is clear that there exists afundamental size limit to the diameter of thermally drawn crystallinemetal wires below which the metal wires become inherently unstable andextremely difficult to control, if not impossible, by currentmanufacturing techniques. Capillary fluid instability poses severechallenges for scale-up manufacturing processes. It is clear that thereexists a fundamental size limit to the diameter of thermally drawn metalwires below which the metal wires become inherently unstable andextremely difficult to control, if not impossible, by currentmanufacturing techniques. There is a great and unmet need to break thefundamental limits and technical barriers to enable a reliable way tomanufacture nanometer sized (diameter from tens to hundreds ofnanometers) crystalline metal wires with a continuous length.

SUMMARY

In one aspect of the invention, a method of thermally drawing fiberscontaining continuous crystalline metal nanowires therein includes thesteps of: (a) forming a preform comprising an inner core comprising thecrystalline metal and an outer cladding, wherein at least one of thecore and cladding having dispersed therein nanoelements; (b) drawing thepreform through a heated zone to form a reduced size fiber; (c) forminga second preform created from a plurality of fibers from the reducedsize fiber of (b); and (d)drawing the second preform of (c) through theheated zone to form another reduced sized fiber having a continuouslength exceeding one meter and containing crystalline metal nanowirestherein having a diameter less than 100 nm. In alternative embodiments,this last process may be repeated one or more times to further reducethe size of the crystalline metal nanowires.

In another aspect of the invention, a method of thermally drawing afiber containing crystalline metal nanowires therein includes forming apreform comprising an inner core having a plurality of individual metalwires surrounded by an outer cladding, wherein at least one of the innercore and cladding comprise nanoelements dispersed therein. The preformis then drawn through a heated zone (e.g., a furnace) to form a reducedsize fiber having a length of at least one meter and containing aplurality of continuous crystalline metal nanowires therein having amaximum cross-sectional dimension less than 100 nm.

In another embodiment, a nanoelectrode array includes a fiber having adistal end and a proximal end, the fiber having a plurality ofcrystalline metal nanowires each with a maximum cross-sectionaldimension less than 100 nm embedded therein and terminating at aplurality of exposed electrodes at the distal end of the fiber, whereinthe distal end of the fiber has a diameter that is << than a diameter ofthe proximal end of the fiber.

In another embodiment, an article of manufacture includes a fiber havinga distal end and a proximal end, the fiber having a plurality ofcrystalline metal nanowires embedded therein, each nanowire having amaximum cross-sectional dimension less than 100 nm, wherein the fiberhas a length exceeding 1 meter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a flowchart illustrating one illustrativemethod of thermally drawing fibers containing continuous nanowires.

FIG. 1C illustrates a cross sectional view of a fiber containingcontinuous crystalline metal nanowires therein.

FIG. 2 illustrates another flow chart illustrating a thermal drawingprocess for creating a fiber according to one embodiment.

FIG. 3 illustrates one exemplary method of creating a nanocomposite coreusing accumulative roll bonding (ARB).

FIG. 4 illustrates a fiber embedded with crystalline metal nanowiresused for cell-based assays.

FIG. 5 illustrates an electrode-embedded fiber cell-based assayplatform.

FIG. 6A illustrates a schematic illustration of a preform made from aSn—Si nanocomposite core and polyethersulphone (PES).

FIG. 6B illustrates a photograph of an experimentally drawn taperedfiber within nanowires made from the Sn—Si nanocomposite.

FIG. 6C illustrates a cross-sectional SEM image of the Sn nanowire.

FIG. 6D illustrates a SEM image of the Sn nanowire after chemicaletching of the PES cladding.

FIG. 6E illustrates a pure Sn microwire with a diameter of about 10 μmafter etching of the PES cladding.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIGS. 1A and 1B illustrate a flowchart illustrating one illustrativemethod of thermally drawing a fiber 50 (seen in FIGS. 1B and 1C)containing continuous nanowires 52 (FIG. 1C). Referring to FIG. 1A, themethod starts with operation 100 where a core 2 is formed with acladding 4 surrounding the core 2. The core 2 is typically a metal,metal alloy, or metal matrix. The core 2 may be crystalline or amorphousmaterial. The cladding 4 jackets or surrounds the core 4 and istypically made from an amorphous material such as a polymer, glass, orquartz, whose viscosity reduces gradually as temperature goes above thematerial's glass transition point. According to the invention, at leastone or both of the core 2 and cladding 4 having nanoelements 6 that areincorporated therein. The nanoelements 6 may include nanoparticles,nanowires, nanoplates, nanoflakes, nanowhiskers or other geometries. Thenanoelements 6 generally are nanometer sized particles wherein theirlargest dimension is 100 nm or less. For example, the nanoelements 6 mayhave a size (e.g., diameter) within the range of 1-100 nm. While thenanoelements 6 may have any number of geometries currently the mostcommonly produced nanoelements 6 are nanoparticles that have sphericalshapes. Of course, other shapes are contemplated to fall within thescope if the inventions described herein.

The core 2 and cladding 4 are prepared separately and then mechanicallyor thermally treated to yield a single nanocomposite preform. As seen inoperation 110 of FIG. 1A, a preform 8 is fabricated, for example, byrolling the core 2 and cladding 4 in a sheet 10. The sheet 10 may beformed from the same material used in the cladding 4. The preform 8 ismuch larger and typically has a diameter on the order of about 1 cmalthough the invention is not limited by the size of the preform 8. Forexample, in FIG. 1A, the sheet 10 may be formed from a glass-basedcladding material that forms a continuous phase with the one or morecores 2 embedded inside (in this embodiment the cladding 4 is alsoglass-based). Typically, vacuum consolidation may be performed inconjunction with high temperatures to bond the cladding 4 to the core 2.While FIG. 1A illustrates the preform 8 being formed with a single core2 it should be understood that the preform 8 may be formed with aplurality of cores 2 (e.g., stacked or bundled cores 2).

The nanoelements 6 may be incorporated into the core 2 or cladding 4using any number of solid and liquid state processing methods used forthe preparation of bulk nanocomposites. These methods includes, forexample, casting, extrusion, melting, sonication (e.g., withultrasound), high-shear mixing, solution-based processes, severe plasticdeformation, electroplating, electro-codeposition, sintering, and thelike. FIG. 3 illustrates the formation of a nanocomposite core 2 usingaccumulative roll bonding (ARB) which is one method. In FIG. 3, in thisparticular embodiment, the nanoelements 6 are dispersed within asolution 16 using an ultrasonic transducer 18 or the like. For example,the solution may include a solvent such as acetone and the nanoelements6 are silicon nanoparticles. The dispersion 20 containing thenanoelements 6 is then deposited on a metal foil 22 using a syringe 24or other applicator. For example, the metal foil 22 may include Sn foil.Next, as seen in FIG. 3, another layer of metal foil 22 is placed on thedeposited dispersion 20 and the entire structure is then introducedthrough a pair of rotating rollers 26 with a small gap to compress thestructure. In the illustrated embodiment, this produces a Sn—Sinanocomposite core 2. A stock Sn—Si nanocomposite can also be producedby electrocodeposition. Cold extrusion, casting, or other methods areused to transform the stock Sn—Si nanocomposite into the desired shapeof the core 2. While FIG. 3 illustrates the formation of a nanocompositecore 2 that includes a metal plus nanoelements 6, in other embodiments,the nanoelements 6 are incorporated into the cladding 4 material.

For the manufacturing of fibers 50 embedded with crystalline metalnanowires (e.g., gold, platinum, or silver), suitable nanoelements 6(e.g., ceramics, oxides, carbides or borides) can be mixed and dispersedinto the metal core 2 in the macroscopic preform 8 to increase theviscosity of the molten metal; it also reduces the interfacial energybetween the liquid metal of the core 2 and material of the cladding 4 tosuppress the fluid instability during thermal drawing, thus allowingfurther size reduction of the metal core 2 to nanoscale sizes. Thenanoelements 6 may also include semiconductor materials, hightemperature metals, carbon, and ceramics. For metals, the presence ofthe nanoelements 6 suppresses the instability that would otherwise forcethe creation of the metal in the nanowires 52 to break and formdroplets; thereby breaking the continuous nature of the elongatenanowire 52. The presence of the nanoelements 6 enables long lengthfibers 50 to be created that have long lengths (greater than 1 meter).As explained herein, the prior art has not been able to generatecrystalline metal nanowires 52 having useful lengths (e.g., greater than1 meter).

Referring back to FIG. 1A, in operation 120, the preform 8 is thenthermally drawn through a furnace 12. The furnace 12 is part of a fiberdrawing furnace which is well known and commercially available. Thefiber drawing furnace operates using a furnace 12 that applies heat tothe preform 8. The preform 8 is typically loaded above the fiber drawingfurnace and upon insertion the preform 8 necks down on its own and thepreform 8 end is cutaway and fixed to a fiber drawing mechanism (e.g.,spool, wheel or the like). The fiber drawing furnaces enables one tocontrol the temperature of the furnace 12 which is set at a designatedvalue above the softening temperature of the glass part of the preform8. The speed of the downward linear motion may be controlled by speed ofthe fiber drawing mechanism. The diameter (or other dimension) of thepulled fiber may be monitored during fiber formation. A load cell may beused as part of the fiber drawing furnace to measure and monitor thedrawing force which is an indicator of fiber quality and processingcondition because it is directly related to the viscosity of thesoftened material at the neck-down area 14. Tension monitoring can beincorporated into the system (along with measured diameter) and used asa feedback signal to adjust or modulate the drawing/feeding speed andtemperature of the furnace 12.

Next, as seen in operation 130, the reduced diameter fibers that havebeen drawn through the furnace 12 are then cut and placed in a bundle 26or stack and then jacketed by the same material 10 that was used tocreate the preform 8 as illustrated in operation 140. This createsanother preform 8′ that is then subject to thermal drawing as seen inoperation 150 in FIG. 1B. The newly formed preform 8′ is run through thefiber drawing furnace as explained above. In this regard, the methodprovides for iterative size reduction as each pass through the furnace12 reduces the diameter of the core 2 to form the wires. In oneembodiment as illustrated in FIGS. 1A and 1B, two passes through thefurnace 12 may be enough to generate a fiber 50 that has continuouscrystalline metal nanowires therein. FIG. 2B illustrates the processends after two passes through the furnace 12 whereby the final fiber 50has the crystalline metal nanowires therein (step 160). The crystallinemetal nanowires have nanometer sized dimensions, namely, a diameter lessthan 100 nm. In some embodiments, the nanowires may have non-circularcross-sectional shapes. In such instances, the longest cross-sectionaldimension of the nanowire would be less than 100 nm. As seen in FIG. 1B(dashed line), optionally, additional preforms 8 may be created afterthe second preform 8′ has been run through the furnace 12. Theadditional preforms 8′ are created as previously explained whereby thedrawn fibers are cut and bundled or stacked and a new preform is formedusing the same cladding material 10. This new or additional preform 8′is then run through the furnace 12 again until the desired final featuresize is achieved.

FIG. 2 illustrates a flowchart illustrating another illustrative methodof thermally drawing a fiber 50 with cross-sectional views of the core2, cladding 4, and preform 8 being illustrated. In this embodiment, afirst preform 8 is formed that includes a core 2 and cladding 4. Thenanoelements 6 are dispersed in the core 2, the cladding 4, or both thecore 2 and the cladding 4. The initial preform 8 is subject to thermaldrawing and cutting as seen in operation 200 which generatessmaller-sized fibers 30. These fibers 30 are then bundled or stacked andwrapped in a cladding 4 to create another preform 8′ and then subject toanother thermal drawing and cutting operation as seen in step 210.Another set of fibers 30′ is created with progressively smaller cores 2and then bundled and stacked and wrapped in a cladding 4 to generateanother preform 8″. The process of thermally drawing and cutting may berepeated any additional number of times as illustrated in step 220 togenerate the final fiber 50 containing the nanowires 52 (FIG. 1C)contained therein.

FIG. 2 illustrates the final fiber 50 that contains a proximal end 32and a distal end 34. As seen in FIG. 2, the distal end 34 of the fiber50 has a cross sectional dimension that is much smaller (<<) than thecross sectional dimension of the proximal end 32 of the fiber 50. Thisconstruction has the advantage in that the proximal end 32 of the fiber50 and the wires 52 contained therein can be easily interfaced withback-end electronic interfaces due to its larger size. Numerousapplications can be enabled by the fibers 50. These include, forexample, applications for thermoelectric generators, battery electrodes,low current fuses, nano-electrode arrays, reinforcement for compositematerials, sensors for material or sample study at the micro ornanoscale, metamaterials or plasmonic materials for telecommunicationapplications.

One particular example of a use for the fiber 50 is for cell-basedassays. In particular, the nanowires 52 that are contained in the fiber50 can terminate at electrodes 54 (FIG. 4) that are formed at the distalend 34 of the fiber 50. The electrodes 54 that are formed at the distalend 34 of the fiber 34 may be active electrodes in which current isapplied to the cell or other sample or, alternatively, the electrodes 54may be passive electrodes that are used more for detection purposes.

FIG. 4 illustrates one such example a fiber 50 that includes anelectrode-embedded fiber with graded dimensions and material compositionbetween the proximal end 32 and the distal end 34. That is to say thefiber 50 includes a distal 34 end having a very small diameter and aproximal end 32 that has a diameter that is much larger than that of thedistal end 34. The distal end 34 of the fiber includes an array 36 ofelectrodes 54 that are exposed and made of biocompatible materials usedfor interfacing with biological cells 300. The dimension of everyembedded wire 52 is gradually increased from nanoscale to macroscale(together with the surrounding insulation tubes) starting from thedistal end 34 that contains the exposed electrodes 54 and movingproximally in the direction of the proximal end 32. In addition, theconstituent metal of the embedded wires 52 can also be changed fromsomething with biocompatibility at the distal end 34 to low resistivityfor high fidelity off-chip signal routing. The wider proximal end 32 ofthe fiber 50 is connected to an interface device 56 that connects to 58control circuitry such as a PCB for signal transmission, signalreceiving, processing, and storage.

The electrode-embedded fiber 50 illustrated in FIG. 4 may be used forcellular electrophysiological measurements with sub-cellular spatialresolution and intracellular phenotyping capability. The electrode 54dimension, inter-electrode arrangement, and material can be designed fordifferent biological cell types and counts. Typically, the electrode 54dimension is significantly smaller than a typical cell size (˜10-100 μm)so as to spatially confine the emanated electric field for highlylocalized measurements as illustrated in FIG. 3 inset. On the otherhand, the electrodes 54 do not need to be unduly small (i.e. <20 nm) asthe goal is to identify and track changes of intra-cellular componentssuch as nucleus, mitochondria, chloroplasts, endoplasmic reticulum,Golgi, and even lysosome.

In the embodiment of FIG. 4, various pairs of electrodes 54 are used toextract the two dimensional spatial impedance distribution along thesurface of the cell. An AC voltage V_(AC1) is applied across the E1-E2pair such that the current emanated from one electrode penetrates theintracellular space above and in between the pair. A higher frequencydirects the trans-cellular current to flow nearer to the top cellmembrane (dashed traces) while a lower frequency does the opposite(solid traces). This is intuitive given that the higher frequency ACcurrent can permeate the cell membrane and some capacitive subcellularcomponents more effectively, and vice versa. As a result, theelectrode-embedded fiber 50 has the ability to perform intracellularphenotyping in the depth (z) dimension by taking differentialmeasurements over several different AC frequencies. Since the currentalways starts and ends with an electrode, the intracellular impedanceright above an electrode can alternatively be extracted by using twonearby electrodes: by applying an AC voltage V_(AC2) across E3 and E5 tomeasure impedance above E4 as shown in the FIG. 4 inset.

For the electrodes 54 in the distal end 34, metals with knownbiocompatibility such as gold and platinum may be used; for theproximally extending remainder of the nano/macro electrodes 54, metalswith low resistivity such as copper or silver may be used as illustratedstarting at the transition 60. For the cladding 4, materials that arebiocompatible, mechanically robust, and electrically insulating such asglass (for drawing high melting point metals) and polymer (for drawinglow melting point metals) can be used. In addition, embedding air orvacuum insulation within the cladding 4 may optionally be used tofurther minimize inter-electrode crosstalk.

The electrode-embedded fiber 50 solves an important biotic/abioticinterfacing problem. Not only is the electrode-embedded fiber 50adaptable to different cell types and counts requiring differentphenotyping resolutions and surface areas, the electrode-embedded fiber50 includes a proximal interface that is amenable to fit the same orsimilar PCB without re-design. In other words, the electrode-embeddedfiber 50 is scalable, cheap and disposable while the PCB and chipset arereusable. The electrode-embedded fiber 50 also takes care of thedimension and material mismatch between the cell phenotyping surface andsampling/processing circuitries. In the larger context, theelectrode-embedded fiber 50 approach generally tackles the nano-to-macrointerfacing challenges for 2D interconnection electrode arrays. Air orvacuum insulation could be embedded inside the fiber 50 toward idealelectrical interconnection with minimal parasitic coupling. Note thatonly the cores of the produced fibers are needed, the cladding materialscan be selectively etched away using organic solvents for polymer or HFsolution for glass or quartz.

FIG. 5 illustrates an electrode-embedded fiber 50 cell-based assayplatform. As seen in FIG. 5, cell culture plates 62 are provided withmultiple wells 64. At the bottom of each well 64, several openings (notshown) are created for the electrode-embedded fibers 50 to plug in andthen seal any resultant gap at the rim. The proximal end 32 of theelectrode-embedded fibers 50 are connected to precision LCR meter(impedance measuring device) to perform impedance spectroscopy duringplatform validation and actual operation. Each well 64 may have a numberof electrode-embedded fibers 50 that terminate or interface with thewell surface. A cell or multiple cells 300 that sit atop the distalelectrode array of the electrode-embedded fibers 50 may have hundreds oreven thousands of separate electrodes that are covered by the cell.

Prior to any cell phenotyping experimentation, the assembled plates areexposed under UV and injected with buffer solution into theelectrode-embedded fiber-plugged cell culture wells to check for leaksand sterility. In addition, one can obtain impedance spectra of thebuffer solution without cells using several pairs of electrodes 54. Thecell-based assay is able to examine cellular morphology, proliferationrate, attachment-adhesion-spreading, and intra-cellular content changes,which are useful early indicators of pharmaceutical or adverse cellulareffects. The assay platform of FIG. 5 allows one to detect and quantifythese cellular events in a real-time, label-free, and non-invasivemanner.

The assay platform allows oncologists to perform assay-directedchemotherapy instead of empirically based therapy, i.e. drug selectionbased on clinical trial evidence. Although in principle many complexfactors may also determine the outcomes of chemotherapy in vivo, the useof the assay platform of FIG. 5 could ultimately replace the multi-wellassays and result in more rational and personalized treatment decisionsin this highly fatal carcinoma disease. Compared to conventional assays,e.g. cell viability assays (MTT and ATP assays), the electrode-embeddedfiber assays can provide more informative cellular data as additionalsafeguards to predict in vivo response.

FIG. 6A illustrates a schematic of the macro preform that wasexperimentally tested with a Sn—Si nanocomposite core and PES cladding.About 2 volume % of Si nanoparticles (NPs) with a diameter of 80 nm wereincorporated into the Sn matrix through electroplating. The macro Sn—Sinanocomposite preform was then cladded with PES for thermal drawing. Theconsolidated preform was fed into a cylindrical furnace at constantfeeding speed (50 μm/sec) at 275° C. with a constant drawing speed ofaround 6 m/min. Next, the drawn fibers were cut, stacked andreconsolidated from the first draw following the procedure shown inFIGS. 1A and 1B. The iterative size reduction enabled by thermal drawinggives rise to the micro-to-nano metal wires. After drawing, some polymercladdings were dissolved in Dichloromethane (DCM) to expose the metalwires for scanning electron microscopy (SEM) characterization. FIG. 6Billustrates a photographic image of the drawn electrode-embedded fibermade from the Sn—Si nanocomposite. FIG. 6C illustrates a cross-sectionalSEM image of the Sn nanowire. As one moves closer to the distal end, thenarrower the wire becomes. FIG. 6D illustrates a SEM image of the Snnanowire after chemical etching of the PES cladding. FIG. 6E illustratesa pure Sn microwire with a diameter of about 10 μm after etching of thePES cladding. In the thermal drawing method, the nanoelementsincorporated either are pushed to the metal/polymer interface duringdrawing, and serve as the interfacial energy modifier, or stay insidethe metal matrix and increase the viscosity of the molten metal.

While embodiments of the present invention have been shown anddescribed, various modifications may be made without departing from thescope of the present invention. The invention, therefore, should not belimited except to the following claims and their equivalents.

1. A method of thermally drawing fibers containing continuouscrystalline metal nanowires therein comprising: a) forming a preformcomprising an inner core comprising the crystalline metal and an outercladding, wherein at least one of the core and cladding havingnanoelements dispersed therein; b) drawing the preform through a heatedzone to form a reduced size fiber; c) forming a second preform createdfrom a plurality of fibers from the reduced size fiber of (b); and d)drawing the second preform of (c) through the heated zone to formanother reduced sized fiber having a continuous length exceeding onemeter and containing crystalline metal nanowires therein having adiameter less than 100 nm.
 2. The method of claim 1, wherein thenanoelements comprise nanoparticles, nanowires, nanoplates, nanoflakes,or nanowhiskers.
 3. The method of claim 1, further comprising forming athird preform created from a plurality of fibers of (d) and drawing thethird preform through the heated zone to form another reduced sizedfiber having a continuous length exceeding 1 meter and containingcrystalline metal nanowires therein having a diameter less than 100 nm.4. The method of claim 3, further comprising forming one or moreadditional preforms created from a plurality of fibers formed by thethird preform and drawing the one or more additional preforms throughthe heated zone to form another reduced sized fiber having a continuouslength exceeding 1 meter and containing crystalline metal nanowirestherein having a diameter less than 100 nm.
 5. The method of claim 1,wherein the nanoelements have a diameter or major cross-sectionaldimension within the range of 1 to 100 nm.
 6. The method of claim 1,wherein the nanoelements comprises a metal or ceramic.
 7. (canceled) 8.The method of claim 1, wherein the core comprises one of gold, platinum,or silver.
 9. The method of claim 1, wherein the cladding comprises apolymer or glass.
 10. (canceled)
 11. The method of claim 1, furthercomprising sintering the reduced sized fiber having metal nanowirestherein.
 12. The method of claim 1, further comprising cutting thefiber, wherein the cut fiber has a distal end and a proximal end and thediameter of the distal end is << the diameter of the proximal end.
 13. Amethod of thermally drawing a fiber containing crystalline metalnanowires therein comprising: forming a preform comprising an inner corehaving a plurality of individual metal wires surrounded by an outercladding, wherein at least one of the inner core and cladding comprisenanoelements dispersed therein; and drawing the preform through a heatedzone to form a reduced size fiber having a length of at least one meterand containing a plurality of continuous crystalline metal nanowirestherein having a maximum cross-sectional dimension less than 100 nm. 14.The method of claim 13, wherein the nanoelements comprise one or more ofnanoparticles, nanowires, nanoplates, nanoflakes, or nanowhiskers. 15.The method of claim 13, wherein the nanoelements have a diameter ormajor cross-sectional dimension within the range of 1 to 100 nm.
 16. Themethod of claim 13, wherein the nanoelements comprises a metal orceramic.
 17. (canceled)
 18. The method of claim 13, wherein the corecomprises one of gold, platinum, or silver.
 19. The method of claim 13,wherein the cladding comprises a polymer or glass.
 20. (canceled)
 21. Ananoelectrode array comprising: a fiber having a distal end and aproximal end, the fiber having a plurality of crystalline metalnanowires each with a maximum cross-sectional dimension less than 100 nmembedded therein and terminating at a plurality of exposed electrodes atthe distal end of the fiber, wherein the distal end of the fiber has adiameter that is << than a diameter of the proximal end of the fiber.22. The nanoelectrode array of claim 21, further comprising a circuitinterface device coupled to the proximal end of the fiber.
 23. Thenanoelectrode array of claim 21, wherein the distal end of the fiber isdisposed in a well, channel, or reservoir of a microfluidic device. 24.The nanoelectrode array of claim 21, wherein the composition of themetal nanowires changes along the length thereof with the exposedelectrodes comprising a first metal and a proximal portion that islocated proximally with respect to the exposed electrodes comprises asecond, different metal.
 25. (canceled)